Vacuum metallizing of plastic and similar dielectric substrates is disclosed in various forms including U.S. Patent:
U.S. Pat. No. 2,992,125 Fustier PA1 U.S. Pat. No. 2,993,806 Fisher PA1 U.S. Pat. No. 3,118,781 Downing PA1 U.S. Pat. No. 3,914,472 Nakanishi PA1 U.S. Pat. No. 4,101,698 Dunning PA1 U.S. Pat. No. 4,131,530 Blum PA1 U.S. Pat. No. 4,211,822 Kaufman PA1 U.S. Pat. No. 4,215,170 Oliva PA1 Thin Film Phenomena, Kasturi L. Chopra, Robert E. Kreiger Publishing Company, Huntington, N.Y., 1979. See especially pp. 163 et seq. PA1 Handbook of Thin Film Technology, Leon I. Maissel and Reinhard Glang, McGraw-Hill Book Company, New York, N.Y., 1970. See especially pp. 8-32 et seq.
Prior U.S. Pat. No. 4,431,711 issued Feb. 14, 1984, relates to metal film island structure and spacing to the appearance and performance of a commercial product, to the conductivity of the metal layer, to the corrosion resistance of the metal layer and/or to the adhesion of the top coat. It further relates to nucleation and film growth to a desired island structure and spacing that achieves these ends.
With regard to the last statement, two excellent reference books are:
These texts discuss and illustrate the stages of metal film growth by vacuum deposition from metal nucleation and nuclei growth, to liquid coalescence, to electrically discrete islands, channelization with incipient film conductivity, and finally, full continuous film formation. Film formation of vacuum deposited metals on plastic substrates for commercial products, especially on elastomeric plastic substrates, is not discussed. Nor is the interdependence of the natures of the metal film and the top coating correlated with product performance.
U.S. Pat. No. 4,431,711 shows the significant difference in performance to be obtained with a vacuum metallized flexible plastic product, top coated, where the metal particles are coalesced only to the island state instead of being allowed to coalesce to beyond the channelization stage where film conductivity is established.
In the '711 patent, the separate islands are coalesced from separate nucleation points and are globular or rounded and fused appearing and are part of the nucleation and growth process.
In general, the coalesced islands forming the indium films of the '711 patent are smaller and there is a much greater spacing between them that can be filled with the resin of the top coating, in effect encapsulating the islands and binding them to the substrate surface. The rounded islands are better protected by the resin and the film over all is far more corrosion resistant, surprisingly so. The metal film is much more securely adhered to the substrate--a very significant advantage. The appearance of the globular island product is better--it is more specular, more reflective.
The construction of the indium island structure in U.S. Pat. No. 4,431,711 includes islands that are separated by channels which receive the top coat to bond the resinous film of the top coat to the substrate for the indium island structures. While the island structures are suitable for their intended purpose, it has been observed that the channels formed between the individual islands also contain many clusters and smaller islands of residual material. It is believed that this material reduces the total effective area of substrate material to which the top coat can be bonded. Consequently, the resultant bright trim article may be subject to undesirable delamination between the top coat and the substrate material.
U.S. Pat. No. 4,713,143 discloses a corrosion resistant vacuum metallized article of bright metallic material in which a dielectric substrate surface has a vacuum deposited layer of metal selected from a group consisting of indium and alloys thereof which alloys are predominantly of indium and wherein the vacuum deposition is continued only until there is a formation of discrete islands which visually appear as a continuous film, but that have channels formed between the discrete islands of a dimension so as to maintain the islands electrically non-conductive over the surface area of the substrate, wherein the process includes etching the vacuum deposited discrete islands with a solvent which slowly dissolves or removes residual amounts of indium from the channels between the distinct islands so as to clear the channels to expose additional bonding surfaces on the substrate for increasing the surface area of adhesion between the substrate and a protective dielectric top coat.
The deposited islands are formed by indium which is amphoteric and thus has some solubility in both acids and bases. As deposited, the indium metal layer is composed of tiny islands ranging from tiny clusters of 25 angstroms or less in diameter. The tiny clusters are barely resolvable in the transmission electronic microscope. The islands can increase in diameter to sizes as large as 4,000 angstroms in diameter. Each of the islands is separated by channels which can be several hundred angstroms wide. However, in the deposition process to form the aforedescribed indium island structure, it is observed that many clusters and small islands of residual indium material may exist in the channels which produce the desired electrically non-conductive characteristics across the surface of the substrate. The process of my '143 patent includes etching the previously deposited indium material with a solution that slowly dissolves or removes the small clusters and islands to clean the channels and thereby define an additional surface area against which the top coat can adhere to the base coat so as to improve its adhesion to the base coat. The typical adhesion strength of a top coat material to a base coat material is in the order of 2 orders of magnitude stronger than the adhesion strength of the top coat to the metal making up the individual island structures separated by the channels. The treatment steps for vacuum deposited islands just before top coating consists of rinsing the part in a 10% NaOH solution for 60 to 90 seconds in a temperature range of 150.degree.-160.degree. F. followed by two water rinses and a second rinse with deionized water. This etch treatment step greatly improves the adhesion of top coat material of the type set forth in U.S. Pat. No. 4,431,711. While the flexible substrate described in U.S. Pat. No. 4,431,711 has sufficient adhesion to pass most automotive specification tests, it is desirable to improve the adhesion in such article so that it will consistently pass an X-scribed type taped adhesion test after either Florida exposures or accelerated weathering tests including (QUV, weatherometer, xenon, dual carbon arc weatherometer). With increasing emphasis on quality in American made cars, such tests are now beginning to show up in automotive specifications (see, for example, Fisher Body FBMS 1-51 specification). While etching the island containing metal layers of the type described in U.S. Pat. No. 4,431,711, an improved adhesion between top coat and base coat materials results so that such X-scribed standards can be met. While suitable for their intended purpose, such articles that are spray coated can have a surface finish that is referred to as either an orange peel surface or spray mottled surface. The effect is due to the failure of either the base coat or the clear coat spray coating to flow to a smooth, level surface. Such lack of smoothness can undesirably reduce the specularity or mirror-like quality of the images visually seen in coatings including the metal film comprised of the island containing layer.
Various methods for smoothly coating articles are known including those set-forth in U.S. Pat. Nos. 3,952,699; 4,312,292; 4,874,639; and 4,919,977.
The '292 patent includes spray coating a tile that is mounted on a rotatable horizontal platform that carries a second rotatable platform for rotating a part to be coated in a second plane that is inclined at an angle to the horizontal.
The '639 and '977 patents are directed to a method for spray coating automobile bodies. The method in the '977 patent includes mounting the bodies on their central axis and rotating the bodies about such axes with respect to spray painting devices. Alternatively, the method set-forth in the '699 patent includes mounting the spray paint devices on a rotating platform and driving the spray guns about the car body. The method set forth in the '699 patent requires careful selection of the wetness of the spray coating to prevent runs on the vertical surfaces of the car body.
None of the aforesaid patents are related to a method for improving the specularity of bright trim parts having a metallic island structure for a chrome like appearance while maintaining a discontinuity across the metal layer in the trim part to prevent corrosion therein. Specifically, the aforesaid patents do not disclose a method for manufacturing a bright trim product having reduced orange peel effect or spray coating mottle so as to improve specularity of a bright metal island film deposition thereon.
Furthermore, none of the aforesaid patents include a reel rotation step that will accommodate the manufacture of a plurality of parts at the same time without requiring separate mounting and rotation of the individual parts on their own axes.